Past Modal Verbs

How do you form the modal verb to represent a past meaning?

Which is the correct order: the level of certainty (most certain - impossible)

should've is a hypothetical modal verb, to criticize past behavior

the negative form of must have is must not have

_______ is used when something was a good idea, but didn't do it.

________ means impossibility in the past, even if you had wanted to do it.

Choose the correct answer: Experts now believe that Mrs. Redwood must've/ might've brought the plague back from India.

Choose the correct answer: The hotel manager must've conspired/ had to conspire with the doctor in some way.

Choose the correct answer: The British Embassy had to investigate/ should have investigated Eleanor's story more fully.

Which is the stressed form of the past modal verb?

What are your biggest problems with past modal verbs? (pick all that apply)